Long Term Evolution-Advanced (LTE-A) system is a further evolved and enhanced 3rd Generation Partnership Project (3GPP) LTE system. In the LTE-A system, in order to meet the International Telecommunication Union (ITU)'s requirement for peak data rate for the 4th generation communication technology, carrier aggregation (CA) is introduced. In the carrier aggregation, frequency spectrum of two or more Component Carriers (CC) are aggregated to obtain a broader transmission bandwidth, wherein each component carrier can be configured to be compatible with LTE system, each component carrier has independent Hybrid Automatic Repeat Request (HARD) procedure; the User Equipment (UE) in LTE-A can simultaneously access multiple component carriers for data receiving and transmitting according to the UE's capability and traffic requirements.
In the 3GPP LTE system, in order to support the technologies including dynamic scheduling, Multiple-Input and Multiple-Output (MIMO) and Hybrid Automatic Repeat Request etc., the terminal needs to feed back Uplink Control Information (UCI) to the base station on Physical Uplink Control Channel (PUCCH), for example: Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), Rank Indication (RI), Acknowledgment/Negative Acknowledgement (ACK/NACK) and Scheduling Request (SR) etc. Wherein, CQI, PMI and RI are generally referred to as Channel State Information (CSI). The system reserves PUCCH for channel state information, hybrid automatic repeat request acknowledgement information and SR respectively, and the UE feeds back UCI on corresponding PUCCH.
In the prior art 1, when the UE needs to feed back ACK/NACK or SR in the LTE-A system, and at the same time the UE needs to send CSI to the base station based on configured CSI feedback periodicity, that is to say when the UE needs to transmit CSI and ACK/NACK on PUCCH simultaneously, or, when the UE needs to transmit CSI and SR at the same time, the UE has to drop all the CSI, and transmits ACK/NACK or SR only on the PUCCH for ACK/NACK or SR.
The study of the prior art 1 founds: under carrier aggregation in the LTE-A system, the probability of simultaneously feeding back CSI and ACK/NACK by UE is high, if dropping all the CSI all the time, in this case: on the one hand, the base station cannot obtain the quality of the downlink channel, so that the base station cannot schedule accurately, and influence the downlink throughput of the system; on the other hand, if dropping all the CSI, in order to obtain the quality of the downlink channel, the base station probably needs to trigger non-periodical CSI feedback of UE by using physical downlink control channel for reporting on Physical Uplink Shared Channel (PUSCH), which will increase system resource overhead.
In the prior art 2, in LTE-A system, when the UE feeds back ACK/NACK according to the downlink data sent from the base station, and at the same time the UE needs to send CSI to the base station based on configured CSI feedback periodicity, that is to say when the UE needs to simultaneously transmit CSI and ACK/NACK on PUCCH, it bundles the ACK/NACK into 2 bits or 1 bit, and then sends them with CSI. The so-called ACK/NACK bundling implements logical AND operation for hybrid automatic repeat request information to be bundled, for example, if the hybrid automatic repeat request acknowledgement information to be feedback for one carrier is ACK and the hybrid automatic repeat request acknowledgement information to be feedback for another carrier is NACK, the result of bundling is NACK. Another example: assume that the number of the downlink aggregate carriers for UE is 2, and the transfer mode for each downlink carrier is closed-loop spatial multiplexing, in this case, the UE needs to feed back hybrid automatic repeat request acknowledgement information for both of these two downlink carriers, and for each downlink carrier, both of the ACK/NACK for the first code word and second code word are needed for feedback. According to the prior art, when the subframe for feeding back CSI also needs to simultaneously feed back ACK/NACK, bundling the hybrid automatic repeat request acknowledgement information, more specifically, bundling the ACK/NACK for the first code word and the ACK/NACK for the second code word for each downlink carrier respectively, and eventually get 2 bits of hybrid automatic repeat request acknowledgement information, the UE transmits the obtained 2 bits of ACK/NACK with CSI in certain way.
The study of the prior art 2 founds: under carrier aggregation in the LTE-A system, there is the circumstance that the channel correlation of several aggregated downlink carriers is low, the low channel correlation of two carriers means that the correlation between correct data and incorrect data transmitted on those two downlink carriers is also low, so that the probability of transmitting the correct data on one carrier and the incorrect data on the other carrier is high, if bundling the ACK/NACK of two carriers all the time, the result will always be NACK, so that there is no need to retransmit the data for both of the downlink carriers. So, bundling ACK/NACK all the time influences system downlink throughput, and increases system resource overhead due to the unnecessary downlink data retransmission.